Heating device



March 30, 1943. R. A. Bu-:RwlRTH HEATING DEVICE Filed May 3l,y 1941 Passed Mu. 3o, 1943 HEATING DEVICE Rudolph A. Bierwirth, Heddon', Heights, N. J., assignor to Radio Corporation of- America, a corporation o! Delaware ApplicatlonMay 31, 1941, Serial No. 395,943

6 Claims.

This invention relates to heating devices, and

- more particularly to a device for heating conductive articles by induction from a source of energy of high frequency.

In many industrial applications, it is necessary. during the manufacture of various articles, to apply heat thereto. In some cases, it is necessary to apply the heat locally and with fair rapidity. One such example is in uniting sheets of metal or other material by means of rivets which are exploded with the ald of an explosive charge in order to effect an expansion of the rivet shank. According to the moet common practice, a heating iron is brought 'into engage ment with the head of the rivet in order to apply heat to the explosive charge. Among the disadvantages of such heating irons are that they must be maintained at a relatively high perature, they require a relativelylong period ci time to bring them up to operating temperatures, they require replacement of heating irons for various articles which require treatment with different degrees of heat, so that e. considerable period oi time is necessarily lost while waiting for hot irons to cool and cold irons to come up to operating temperatures, and they have a short life..

The primary object or' my present invention is to provide an improved heating' device :for industrial applications such as that noted alcove, which device will not he subject to the dis-ad vantages of similar prior art devices,

More particularly, it .is an object o my present invention to provide improved heating device which is capable of applying heat locally in a small area.

A further object oi my invention is to provide an improved heating device as aforesaid which is comparatively simple in construction and easy to handle.

in accordance with my invention, i provide a single turn coil which is irusto-corlical in shape and couple the coil to a high frequency oscillaM tor through a step-dovvn transiormer, the apex area of the coll being of small diameter (for example, of the order ot the diameter of a rivet head). The oscillator may supply to the transformer about 300 to i000 Watts at frequencies in the neighborhood oi from 30G irc. to 400 kc. il high current is induced in the secondary circuit, which includes the frusto-conical coupling coil, the latter setting up a highly concentrated magnetic ileld at its apex endrso that, when it is brought into proximity with a metallic object, the latter will become heated by reason of the eddy currents induced therein. The advantage of using a frusto-conically shaped coil is that a small spot may be heated in a at surface while enough metal is provided to carry away the heat generated in the coil itself. if desired, a suitable air blastl may be provided to assist in coupling coll.

The novel features that I consider characteristic of my invention are set forth with particularity ,in the appended claims. The invention, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description, when read in connection with the accompanying drawing, in which- Fig. 1 is o. view, partly in section, of a heating device formed according to my present invention and coupled 'to a suitable source oi energy,

Fig. 2 a sectional View taken on the line ii-uil of Fig. l,

Fig. 3 is a tcp plan view of the coupling or heating coil,

is a side elevation thereof, and

Fig. 5 is a top plato view of a modified form oi coupling coil.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is chou/n a tubular supporting member l oi insulating nia terial on which is wound the primary Winding il ci' a transformer coupled 'to a suitable high in," quency oscillator hy a concentric cable l. rounding the primary Winding e and spaced therefrom by a plurality of clrcumerentielly distributed, longitudinally disposed, insulated spacing members c is the secondary winding it or the transformer. The primary Winding t may consist of 56 turns of No. 14` wire Wound in a single layer on the supporting tube l, and the secondary Winding il may be made of a copper sheet about one-eighth inch thick. and about four inches long, being formed into a tube which surrounds and is concentric with the primary winding 3, as clearly shown in Figs. l. and 2. The longitudinally extending terminals lla of tice secondary Winding l l are, of course, in slightly spaced relation, and secured to the terminals ila. as by rivets, solder, screws, or the like, are the terminals @3a of a single turn, frusta-conical coupling coil i3 having a small diameter at its apex end itc, the axis of the coil i3 being angularly related to the axis of the concentric windings 3 and il.v As clearly seen from Fig. 1, the coupling coil I3, which may also be made from a strip of sheet copper, is so disposed relative to frusto-conical cooling the the secondary winding II that its apex end IIb is most remote from the axis of the coils 3 and Il, whereby the apex end I3b is disposed in advance of the tubular winding II and nearest to the article to be heated.

When the system is set up for operation, the oscillator l supplies energy to the primary winding 3 wherebya high current is induced in the secondary winding Il and thecoupling coil I3 connected thereto. Since the coil I3 is of small diameter, particularly at its apex and Ilb adjacent to which most of the current flowing in the coil I3 is concentratedthere isset up at the apex end of the coil I3 a highly concentrated magnetic field. If, now, the coil I3 is brought into proximity with the head of a rivet Il which is intended to unite a pair of sheets I'I and I. the rivet I5 will become heated because of the eddy currents induced therein by the aforementioned highly concentrated magnetic field. These eddy currents will be sufficient to explode a charge of explosive which has previously been placed in the hollow shank of the rivet I5 to thereby cause the rivet shank to expand slightly, as shown at Ita in Fig. 1, thereby firmly uniting the sheets I1 and I9. The comparatively large area of the coil I3 in relation to the relatively small area thereof adjacent to its apex end I3b where most of the current therein is concentrated permits the heat generated therein to be conducted away fairly rapidly. However, if desired, an air blast produced by a blower 2| maybe fed through a tube 23 into the supporting tube I, down to the coupling coil I3, 4as shown by the solid arrows in Fig. 1, to help cool the coil I3, and also back around the tube I into the space 25 between the primary winding 3 and the secondary winding II,

as shown by the dotted arrows, whereby to coolY the winding 3 as well.

From the foregoing description, it will be apparent to those skilled in the art that I have provided an improved heating device which is capable of being energized by a high frequency source and which is capable of applying heat locally and with great efficiency to an' article to be heated. Since the device is very light in weight and does not itself become appreciably hot, it is easy to handle even over extended periods.

Although I have shown and described but one embodiment of my invention, it will be apparent to those skilled in the art that many changesfin the particular modification described, as well,as other modifications, are possible. For example, insteadl of making the coupling coil frusto-oonlcal in shape, it may be made of any other suitable shape and with its two ends either of the saine.y or different diameters, as may be found most de-r sirable. Also, instead of disposing the coil I3 with its axis as shown in Fig. I, it may be arranged so that its axis is otherwise related to the axis of the coils. Thus, in another form of heating unit, I have arranged the coil I3 so that it extends forwardly of the secondary winding Il with its larger base substantially in augment with the forward end of the winding II and its apex end in front of this winding, the axis of the coil I3 being at an acute angle with the axis of thewindingsland II. Itisalsopossib1e,ifde sired,toformone -ormoreradialslits Ilcinthe coil I3 extendingfromthelargerdiame'terthereofintowarditsapexendssshowninl'immfor e'xample,wherebytofurtherimuxeconcentration of the high current flowing therein almost eng tirely around its apex end. Hore'oven if dired. a suitable shield may be placed adjacent the terminals Ilaofthewinding ll,whichwillincreaae the efficiency of the unit. Theseuand many other changes of a similar nature which will undoubtedly readily suggest themselves to those skilled in the art are possible within the scope of my invention. I therefore desire that my invention shall not be limited except insofar as it is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. An electrical heating device comprising s transformer having primary and secondary windings arranged on a common axis, said primary windingbeing adaptedtobeconnectedioa'source of electrical energy, and a truste-conical coupling coil connected to the terminals of said secondary winding, the axis of said coupling coil being angularly related to the axis of said windings.

2. An electrical heating device comprising an insulated tubular supporting member. a winding thereon constituting the primary winding of a transformer adapted to be connected to a source 0f electrical energy, a single turn, tubular, conductive member surrounding said primary winding, said member constituting the secondary winding of said transformer, and a single turn coupling coil having terminals connected to the terminals of said secondary winding, said coil being frusto-conical in shape whereby the current which may flow therein will be concentrated mostly in a region adjacent to its apex end, and the axis of said coupling coil being angularly related to the axis of said windings.

3. A heating unit according to claim 2 characterized in that theapex end of said coupling coil ismost remote from the axis of said windings.

, 4. An inductor coil comprising a frusta-conical member having terminals for connection to a source of electrical energy, said member being provided with a plurality of slits extending from the larger end thereof toward its apex end whereby most of the current which may flow therein will be concentrated ln an area in the vicinity of the apex end thereof. g

` 5. An inductor heating coil comprising a frustaconical member having terminals for connection to a source of electrical energy, said member being provided with a plurality of slits extending from the larger end thereof toward its apex and whereby most of the current which may now therein will be concentrated in an area in the vicinity of the apex end thereof, and said member having an area which is large compared with said first Anamed area whereby the heat generated therein by said current will be readily dissipated.

6. An inductor coil-according to claim 5 characterized in that said slits are arranged radially. on said coil.

RUDOLPH A. BIERWIRTH. 

